The objective of this research is to elucidate the relationships between structure and function for the placental protein hormone, human chorionic somatomammotropin (HCS or HPL). The functional requirements of the primary, secondary, tertiary and quaternary structures of the protein will be assessed with regard to somatotropic, lactogenic, immunochemical and membrane-receptor activities. In addition to physical measurement of structural parameters of the native hormone by absorption, fluorescence, and circular dichroism spectroscopy, as well as sedimentation, viscosity, electrophoretic and chromatographic behavior, the effects which chemical modifications of the primary structure have on both structure, structural rigidity and function will be evaluated. The modifications employed will include reoxidation of the reduced protein, modification of the single tryptophan residue and iodination of tyrosine residues. Radioactive HCS will be prepared by reduction of the iodinated hormone via catalytic tritiation. The biological profile of the tritiated molecule as well as tritiated forms containing additional chemical modifications will be assessed by bioassay, and radioimmunoassay as well as by membrane-receptor assay procedures. Isolation and structure-function analyses of fragment(s) from plasmin and tryptic digests will be carried out using procedures similar to those employed for HGH.